[cadillac_al]

Do you think your speedometer/odometer are accurate? Since you had a gear swap something could be off and you are actually getting normal mileage. I have always kept track of my mileage on almost every tank of fuel in my trucks since 2000. My K20 always got 10mpg, never on the highway. My K10 always gets 11 mpg in town or highway. Those are both th350 trucks. With a th400 I would bet they would be 1 mpg less.

Sometimes when I get on a stretch of interstate i like to check my odometer with the mile markers to see how accurate it is. One of my Caddys records 85 miles per hundred miles driven. It makes the mileage seem worse if you don't calculate the odometer error.